DESCRIPTION: Despite substantial advances in the treatment of childhood acute lymphoblastic leukemia (ALL), approximately 35 percent of children with this disease will relapse or fail induction therapy. The applicant has observed that endogenous production of tumor necrosis factor-alpha (TNF) by pediatric ALL cells may be linked to refractory disease. Growth of leukemic cells by the majority of patients tested was inhibited by TNF in a dose-dependent manner and was accompanied by apoptosis. In contrast, cells from a subset of patients produced TNF and were resistant to the inhibitory effects of exogenous TNF. Leukemic cell lines derived from TNF-producing, TNF-resistant (TNF+) cells and from TNF-nonproducing, TNF sensitive (TNF-) cells retained the responsiveness of the primary cells to exogenous TNF. Both TNF+ and TNF- lines expressed p60 and p80 TNF receptors (TNFrs), suggesting that phenotypic differences in TNF response between these lines are not due to altered expression of TNFrs. Preliminary experiments indicate marked differences between TNF+ and TNF-cells in the regulation of certain apoptosis/survival associated genes after genotoxic treatments. Moreover, clinical data suggest that the TNF+ phenotype is associated with refractory disease and poor prognosis: The percentage of patients remaining in complete remission at one year post-diagnosis was 20 percent for TNF+ ALL cells vs 89 percent for TNF- ALL. He hypothesizes that endogenous TNF acts as a survival factor for TNF+ ALL cells, protecting these cells from apoptosis. To test the hypothesis, he proposes the following specific aims: 1) To further investigate the response of TNF+ and TNF- ALL cell lines to exogenous TNF, adriamycin, and IR by examining differences in expression of apoptosis vs. survival genes following DNA damage; 2) To determine if blockade of endogenous TNF production (using a TNF-antisense expression construct) affects the response of TNF+ ALL cell lines to exogenous TNF, adriamycin, and IR; 3) To investigate the effects of induction of endogenous TNF (using a TNF expression vector) on the response of TNF- ALL cell lines to these agents; 4) To examine primary leukemic cells fro pediatric ALL patients for expression of TNF and TNF receptors, and to correlate this data with clinical response and in vitro response to genotoxic agents; 5) To determine the cytotoxicity of a recombinant TNF-Pseudomonas endotoxin (TNF-PE) for TNFR+ ALL cells in vitro as well as in the SCID model for engrafted leukemia.